Lighten Up!

A group of coworkers whose conversation reveals they are only interested in partying after work and their parade of boyfriends say this frequently to a self-sufficient young woman whose hobbies include gardening, ice skating, choral singing, ballroom dance, reading, sewing, and photography (she's a real artist there). I wonder what they mean exactly by telling her to "Lighten up!"

Some possibilities:

1 Be less interesting...you make us look bad.
2 Be like us...your choices make us feel bad.
3 Be less cool...we're trying so hard over here.

Truly, these advice givers are only trying to help. They really do think she's living a boring life. That's called irony.